Ultraviolet absorption of flavonoids III. Ionization constants of the 5-hydroxy group in 5,x-dihydroxyflavones
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The ionization constants of the hydroxy groups in 5-hydroxy-, 3,5- and 4′,5-dihydroxy- and 3-hydroxy-5-methoxyflavones and in 5-hydroxy-7-methoxyflavanone have been determined. It has been shown that because of intramolecular hydrogen bonding the 5-hydroxy group has a reduced acidity. However, the capacity for ionization of the 5-hydroxy group changes under the influence of hydroxy groups introduced into the 3, 4′, or 7 positions, and also on passing to the flavanone series.
KeywordsFlavone Hydroxy Group Intramolecular Hydrogen Bonding Flavanone Chrysin
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